(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to form a metal plug structure.
(2) Description of Prior Art
Metal plugs, located in contact, or via holes, are being used in the semiconductor industry, as conductive conduits between underlying and overlying conductive elements of a semiconductor device. The excellent electromigration resistance, as well as the low resistivity of tungsten, have made tungsten an excellent material for the metal plug structures. However to adequately use tungsten as a plug material, adhesive, and barrier layers, have to be employed between the tungsten plug, and the surfaces of the contact or via hole. An underlying adhesion layer, such as titanium, coating the surface of the contact or via hole, formed in an insulator layer, provides the needed adhesion, while an overlying barrier layer, formed between the adhesive layer, and the tungsten layer, protects exposed materials from the reaction products created during the tungsten deposition procedure. Chemical vapor deposition, (CVD), procedures, used to deposit a barrier layer such as titanium nitride, provides improved conformality, or coverage, along the sides of a deep, narrow diameter opening, when compared to titanium nitride layers obtained via plasma vapor deposited, (PVD), procedures. However CVD titanium nitride, barrier layers present difficulties such as providing a poorer nucleation site, for the subsequent, overlying tungsten layer, when compared to PVD titanium nitride layers. In addition aging effects of CVD titanium nitride layer, result in unwanted resistance increases.
This invention will describe a novel composite adhesive-barrier layer, for use with CVD tungsten plugs. Featured in this invention is the deposition of a CVD titanium nitride barrier layer, on an underlying PVD titanium adhesive layer. After subjecting the CVD titanium nitride layer to an anneal cycle, performed in a hydrogen/nitrogen ambient, used to reduce the aging phenomena occurring with CVD titanium nitride layers, a thin PVD titanium nitride layer is deposited, providing the needed nucleation sites for an overlying tungsten deposition. Prior art, such as Ngan et al, in U.S. Pat. No. 5,882,399, describe a titanium-titanium nitride-titanium nitride, composite layer, as a barrier layer protecting aluminum based layers. That prior art however is not applied to narrow diameter contact holes, where a CVD barrier layer, used in this present invention, but absent in this prior art, is needed for conformality, or step coverage. Additional prior art, such as Tsai et al, in U.S. Pat. No. 5,833,817, does apply a titanium-titanium nitride composite layer, along the sides of a contact or via hole, however this prior art uses only a PVD titanium nitride layer, unlike the composite layer described in this invention featuring a annealed, CVD titanium nitride layer, capped with a thin PVD titanium nitride layer.